Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $195.68   3.511%   $202.5503   $202.55   $202.55   $202.60  
  Purchase #2 $21.44   10.671%   $23.7279   $23.73   $23.75   $23.70  
  Purchase #3 $63.76   4.163%   $66.4143   $66.41   $66.40   $66.40  
  Purchase #4 $190.29   5.781%   $201.2907   $201.29   $201.30   $201.30  
  Purchase #5 $201.58   9.558%   $220.847   $220.85   $220.85   $220.80  
  Purchase #6 $77.89   13.136%   $88.1216   $88.12   $88.10   $88.10  
  Purchase #7 $150.99   3.172%   $155.7794   $155.78   $155.80   $155.80  
  7 purchase totals = $901.63       $958.7312   $958.73   $958.75   $958.70